Rehearsing the First Night of the Proms - what's in a note?

Never one to obey convention, Janacek set his Mass in Old Church Slavonic (Glagolitic) and it is just one of many nature-inspired pieces he wrote towards the end of his life. He viewed the Mass as taking place in an outdoor cathedral, made from trees with stars for candles. It is a wonderfully unique and uplifting work and one the BBC SO has played quite a few times over the years. It isn't easy and just when you think you know a piece, someone comes along and says: 

So, who's right? Do we believe the publisher (who often knew the composer at first hand) or the scholar who has dug up original manuscripts and gone back to the composer's initial thoughts?

This has intrigued some great minds. We work a lot with composer/conductors at the BBC Symphony Orchestra and it's always interesting having them conduct their own material and observing the changes they make to it during rehearsals, reminding us perhaps that a piece of music is a living thing. Curiously Pierre Boulez (a composer who is a serial reviser of his own works and with whom we last performed the Glagolitic Mass) prefers original versions of pieces (Stravinsky ballets for example) whereas Oliver Knussen prefers final revisions.

Composers are probably more prone to tinkering with their work post publication than in most other Art forms. Janacek was no exception. In the case of the Glagolitic Mass, which we will be playing tonight to open the 2011 BBC Proms, it may surprise you to learn that there are at least three different performing versions now on the market of a work composed only 84 years ago. We are playing the latest one, published by Barenreiter Prague just this year. Some believe he made changes during rehearsals because it was too difficult for the Brno orchestra playing the 1927 premiere; others claim that the orchestra was in fine shape and that he deliberately altered things for his own artistic reasons. Who knows...

I'll be honest, I didn't know what the differences were until it was too late. At the first rehearsal Jiri Belohlavek said good morning and launched into the beginning of the piece conducting 3 beats to a bar. My part was in 5/8 and the bars had septuplet quavers. This left me reaching for my slide rule... Apparently this was what Janacek (a fan of multiple time signatures) originally intended, rather than the easier sanitised revision in 3/4. Fortunately the BBC SO is pretty good at playing seven notes in the time of five (divided by three) and once we had played it a couple of times the worry lines on our Bohemian conductor's brow relaxed and he uttered his highest words of praise: 'Chapeau', whilst doffing an imaginary cap.

I'm sure even Janacek would have been pleased and wouldn't have changed it for the world. Maybe...

• Find details of tonight's Prom
• Read Janacek's biography